To determine which of the statements regarding the angle of contact and the forces involved in fluid mechanics are correct, we can analyze the concepts of cohesive and adhesive forces, as well as the implications of different angles of contact.
### Step-by-Step Solution:
1. **Understanding Cohesive and Adhesive Forces**:
- **Cohesive Force**: This is the force of attraction between molecules of the same substance. For example, in a liquid, the cohesive forces are the intermolecular forces that hold the liquid molecules together.
- **Adhesive Force**: This is the force of attraction between molecules of different substances. For example, the adhesive force is the attraction between liquid molecules and the molecules of the container (like glass).
2. **Analyzing the Angle of Contact**:
- The angle of contact (or wetting angle) is the angle formed between the tangent to the liquid surface and the solid surface at the point of contact.
- If the angle of contact is less than 90 degrees, it indicates that adhesive forces are stronger than cohesive forces, leading to the liquid wetting the surface.
- If the angle of contact is greater than 90 degrees, cohesive forces are stronger, and the liquid does not wet the surface.
3. **Effects of Changing Cohesive and Adhesive Forces**:
- When cohesive forces increase, the angle of contact becomes obtuse (greater than 90 degrees), indicating that the liquid is less likely to wet the surface.
- Conversely, when adhesive forces increase, the angle of contact becomes acute (less than 90 degrees), indicating better wetting.
4. **Special Case of 0 Degrees**:
- At 0 degrees, the cohesive and adhesive forces are equal, leading to a perfectly wetting situation. This situation is rare and typically not the case in practical scenarios.
5. **Conclusion on Correct Statements**:
- Based on the analysis, we conclude that:
- If the angle of contact is less than 90 degrees, adhesive forces dominate (correct).
- If the angle of contact is greater than 90 degrees, cohesive forces dominate (correct).
- The statement about the angle being 0 degrees indicating equal cohesive and adhesive forces is not correct.
### Final Answer:
The correct statements are:
- A: Angle of contact less than 90 degrees indicates adhesive forces are stronger.
- B: Angle of contact greater than 90 degrees indicates cohesive forces are stronger.
